The present invention relates to rotary veneer lathes, and in particular, a method and an apparatus that minimize the waste veneer cut after a peel break by coordinating the contour of the previous peel spiral with the motion including the path, speed, and position of the knife as it reengages the surface of the rotating log from which the veneer is cut.
A rotary veneer lathe includes means to rotate a log or block about its longitudinal axis and means to advance a knife into the surface of the block to cut veneer from it. The edge of the knife extends along the length of the block and is advanced into its surface at a rate that causes the peeling of veneer of a uniform predetermined thickness. A conventional rotary veneer lathe accomplishes this task by monitoring the angular displacement of the rotating block and advancing the knife a distance equal to the desired veneer thickness with each rotation of the block.
During a production operation, it is frequently necessary to interrupt and later resume peeling veneer from the same block. An interruption in peeling is called a "break," and a resumption of peeling is called "reentry." The break and reentry process has been accomplished traditionally by, respectively, stopping and restarting the advance of the knife at the rate that provides the desired veneer thickness. This procedure causes significant waste in the form of a long taper at break on the trailing edge of the veneer as the knife cuts free from the block, and at reentry on the leading edge of the veneer as the knife reengages the block. The amount of waste is nominally one circumference of the block for each veneer taper generated.
A veneer lathe control system for reducing the amount of waste veneer cut during break and reentry is described in U.S. Pat. No. 4,287,462 of Beck et al. The control system of the Beck et al. patent monitors the angular displacement of a rotating block and stores in a memory the orientation of the radial point on the block from which the knife exits during a peel break. The knife rests at a standby location that is spaced from the peel break location on the block surface by a distance that is an integer multiple of the thickness of the previous peel spiral. The control system guides the knife from the standby location at a peel rate corresponding to the thickness of the previous peel spiral to reengage and resume peeling of the block at the radial point stored in memory.
The Beck et al. control system suffers from the disadvantage that a reduction in waste veneer is realized only when there is no change in peel thickness from break to reentry. There is no means for modifying the knife approach path or its reentry point to promote the cutting of continuous veneer at the largest possible block radius whenever the peel thickness after reentry differs from that before break. This deficiency is especially important in the situation in which the thickness of veneer peeled before break is less than that peeled after reentry. The excessive number of block rotations required to reach continuous veneer of the desired thickness necessitate that the knife reengage the block at a location which minimizes the amount of waste veneer cut in this situation.